1. Field of the Invention
This invention relates to picture size conversion methods and devices that convert pictures in sizes, especially motion pictures, which are displayed on screens of image display systems such as television receivers.
This application is based on Patent Application No. Hei 9-347044 filed in Japan, the content of which is incorporated herein by reference.
2. Description of the Related Art
Conventionally, there are provided a variety of technologies for picture display methods and picture-size reduced display methods.
For example, Japanese Patent Application, Publication No. Sho 64-51774 discloses the technology that thins out picture data in response to a denominator of a fraction of a reduction ratio, which is an even number or an odd number, with respect to each of odd-numbered fields and even-numbered fields. However, this technology cannot achieve the reduction ratio which is designated arbitrarily.
Japanese Patent Application, Publication No. Hei 2-254883 discloses the technology that displays vertically reduced pictures, which are reduced in sizes in a vertical direction of the screen, by reducing a horizontal scanning period to xc2xd of the normal one. However, this technology requires a increased number of scanning lines, which is increased double as compared with a normal number of scanning lines.
Japanese Patent Application, Publication No. Hei 2-33282 discloses the technology regarding the television signal processing system that is capable of performing multiplex transmission on a plenty of information within the predetermined frequency band. This publication merely proposes a method to effectively improve existing television signals. So, it lacks description regarding compression of picture sizes.
Japanese Patent Application, Publication No. Hei 5-284422 discloses the technology to solve the problem due to the time difference between two fields by delaying the odd-numbered field or even-numbered field by one horizontal scanning period. However, this technology has a problem that the delay circuit is complicated in configuration.
Japanese Patent Application, Publication No. Hei 6-86236 discloses the technology to convert analog interlaced scanning signals to analog sequential scanning signals.
Japanese Patent Application, Publication No. Hei 9-130675 discloses the technology to simultaneously display a plenty of reduced pictures on the screen. According to this technology, pseudo frame signals are produced based on video signals belonging to one field, so that resolution is maintained at a reduced picture display mode.
Japanese Patent Application, Publication No. Hei 9-219820 discloses the technology that by using the algorithm to designate lines which are thinned out, thin-out operations are performed with respect to both of the odd-numbered fields and even-numbered fields in such a way that the thinned lines are uniformly arranged.
Moreover, Japanese Patent Application No. Hei 9-106017 (which is filed in U.S. as well as Ser. No. 09/060,560) discloses an example of a motion picture size reduction device. FIG. 13 shows a configuration of the aforementioned motion picture size reduction device.
The motion picture size reduction device of FIG. 13 is configured by a size conversion table creation block 1001, a size conversion table memory 1002, a compressed picture decode block 1003, an original picture frame buffer 1004, a size color conversion block 1005, a converted picture frame buffer 1006, a display control block 1007 and a display unit 1008.
In the motion picture size reduction device of FIG. 13, the compressed picture decode block 1003 converts input original pictures of field form to original pictures of frame form, which are then stored in the original picture frame buffer 1004. If the original pictures of the frame form are subjected to display without being reduced in sizes, they are subjected to conversion made by the size color conversion block 1005, so that converted pictures are stored in the converted picture frame buffer 1006. Then, the display control block 1007 reads the converted pictures, stored in the converted picture frame buffer 1006, to display them on the screen of the display unit 1008.
If the input original pictures are subjected to reduction, a reduced size is designated, so that the size conversion table creation block 1001 creates a size conversion table, which is then stored in the size conversion table memory 1002. At this time, a reduction mode is designated as well. The size color conversion block 1005 makes reference to the size conversion table with respect to each of horizontal lines. Based on results of the reference, the size color conversion block 1005 reads the original pictures corresponding to the horizontal lines. Then, it performs color conversion on the read original pictures to produce converted pictures, which are then stored in the converted picture frame buffer 1006.
In the above operations, the size conversion table creation block 1001 does not make consideration on whether the input original pictures correspond to picture signals of frame form or picture signals of field form. For this reason, the aforementioned device reduces the original pictures by uniformly thinning out data of selected lines from picture data of one frame.
The aforementioned motion picture size reduction device suffers from the problem as follows:
When displaying motion pictures in a picture size reduced manner, distortions occur on reduced pictures, which is shown in FIG. 14A and FIG. 14B. FIG. 14A shows a picture representing a circle which is motionless. In the field form of pictures in which one frame is configured by combining two fields, when the above circle travels on the screen at a high speed, a certain time difference exists between two lines disposed in a vertical direction. In general, such a time difference is {fraction (1/60)} second. FIG. 14B shows a result of process to uniformly thin out lines, wherein the circle is displayed using a odd-numbered field and an even-numbered field. Herein, a contour of the xe2x80x9ccirclexe2x80x9d figure gets blurred or distorted.
It is an object of the invention to provide a picture size conversion method and a picture size conversion device, each of which is capable of avoiding deterioration of picture display quality such as a blur and distortion especially with respect to motion pictures of interlaced display method which are reduced in sizes.
This invention provides a picture size conversion method (and device) to avoid deterioration of picture display quality such as a blur and distortion, especially with respect to motion pictures which are displayed in accordance with an interlaced display method.
A size conversion table storing display flags are created in accordance with a reduction ratio which is designated in advance or which is calculated based on the original picture size and converted (or reduced) picture size. Each of the display flags represents a decision whether to allow display with respect to each of horizontal lines. At first, the method discriminates whether the reduction ratio belongs to a first range or a second range, while the method also discriminates whether each of horizontal lines belongs to an even-numbered field or an odd-numbered field within one frame. In the case of the first range of the reduction ratio which is relatively small, the method thins out all of horizontal lines belonging to the even-numbered field while selectively thinning out horizontal lines belonging to the odd-numbered field with reference to the size conversion table. In the case of the second range of the reduction ratio which is relatively large, the method does not at all thin out the horizontal lines of the even-numbered field while selectively thinning out the horizontal lines of the odd-numbered field with reference to the size conversion table. Thus, original pictures can be converted (or reduced) in sizes in different ways in response to the first range and second range of the reduction ratio respectively.
In addition, it is possible to further create a correction position table storing correction flags each representing whether to perform correction on each of the horizontal lines of the odd-numbered field that is not thinned out in the case of the second range of the reduction ratio. As the correction, a filter process is performed with respect to the aforementioned horizontal line(s). Thus, it is possible to further improve the picture display quality, especially with respect to the motion pictures which move on the screen at a high speed.